Method of producing tunnel diodes by double alloying



1966 TERUO HAYASHI ETAL 3,

INVENTORS 72mm HAY/45H! BY M5451 Mvmmas United States Patent 3,276,925METHOD OF PRODUCING TUNNEL DIODES BY DOUBLE ALLOYING Teruo Hayashi andHisashi Watanabe, Tokyo, Japan, as-

signors to Nippon Electric Company Limited, Tokyo, Japan Continuation ofapplication Ser. No. 71,800, Nov. 25, 1960. This application July 9,1964, Ser. No. 382,693 Claims priority, application Japan, Dec. 12,1959, 34/ 38,954 4 Claims. (Cl. 148-177) This invention relates to anovel semiconductor element of the Esaki type, and is a continuation ofour copending application Ser. No. 71,800, filed Nov. 25, 1960, nowabandoned.

The semiconductor element utilizing the tunnel efiect is based upon thephenomenon that electrons penetrate from one side of a P-N junction tothe other as a result of the quantum mechanical tunnel effect. If theimpurity concentrations of a P region and an N region forming a P-Njunction of a semiconductor are increased until degeneration, thetransition region width of the P-N junction is decreased greatly. Sincethe internal electric field produced at the junction becomes very largewithout the application of an external electric field, the probabilityof electrons penetrating, due to the Zener emission, from the valenceband to the conduction band, or vice versa, is large. If an externalelectric field is applied to the semiconductor, its current-voltagecharacteristics in the forward direction will show a kind of dynatroncharacteristic which can be used for HF oscillation, amplification, andswitching. These characteristics are associated with the tunnel diode.

The gain band width of an Esaki element is inversely proportional to theproduct of the negative resistance of the element and the transitioncapacitance which exists parallel to the negative resistance. Theswitching speed of the diode is also inversely proportional to itsnegative resistance.

Accordingly, it is necessary in the manufacture of the Esaki diode toselect a semiconductor whose effective electron mass is as small aspossible and to make the impurity concentration of the P domain and theN domain of the semiconductor as large as possible, for example, in theorder of -l0 /cm. depending upon the semiconductor. Since the amount ofimpurity which can be diffused into the semiconductor is determined byits solubility and crystal preparation process, many difiiculties areencountered in obtaining a suitable semiconductor single crystal.

In accordance with the invention, the impurity concentrations of the Pand N domains is relatively easily formed by an alloying process,wherein a predetermined amount of impurity is added to the alloy toobtain an impurity concentration in the order of 10 -10 /cm.

The above mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will be best understood by reference to the following descriptionof an embodiment of the invention taken in conjunction with theaccompanying drawing, wherein the drawing is an enlarged cross-sectionalview of the novel semiconductor.

In the drawing, 1 is a part of a small piece properly cut from an N typegermanium single crystal of a low 3,276,925 Patented Oct. 4, 1966specific resistance. On the surface of the crystal 1, a small piece ofindium containing a particular amount of arsenic is alloyed by theconventional alloying process to form an N type region 2 with a highimpurity concentration in the order of 3X10 /cm. The alloy on the upperpart is then removed from the surface of the germanium crystalpreferably by the mercury amalgamation process leaving only the parts 1and 2. In this case, if a material, such as indium, which does not forman eutectic alloy with germanium, is selected as a main constituent ofthe alloy, and if the alloy is formed at a comparatively hightemperature, the thickness of the recrystallized semiconductor can beeasily made in the order of 50-60 microns, and the surface of therecrystallized part may be made smooth.

The germanium body with the region of high impurity concentration isalloyed again, after surface treatment, with a small amount (pellet) ofindium containing a particular amount of a P type impurity, such asgallium. In the drawing, 3 is the P type region having an impurityconcentration of 5 l0 /cm. 4 represents the indium gallium alloy,employed in the last alloying process, which may be used for connectinga lead 6. Also, in this alloying process, an alloy 5, for example, oflead-antimony is alloyed at the same time to form the base electrode, towhich a base lead 7 is connected.

There has now been explained an example embodying the features of thisinvention with N type germanium; it is apparent, however, that the sameprocess could be utilized for a semiconductor other than germanium, forinstance, silicon, intermetallic compounds, and others.

What is claimed is:

1. The method of producing a tunnel diode comprising the steps of:alloying a metal containing an impurity of a given conductivity type toa surface region of a semiconductor body of the same type conductivityto form a degenerated semiconductor region having a high impurityconcentration, said metal being selected to be non-eutectic With saidsemiconductor body; removing a substantial portion of said alloy toexpose the said high impurity concentration region; and alloying a metalcontaining an impurity of the opposite conductivity type to the saidhigh impurity concentration region to form a second opposite type highimpurity concentration region.

2. The method claimed in claim 1, in which the semiconductor body isN-type, the first recited impurity is a donor impurity, and the secondrecited impurity is an acceptor impurity.

3. The method claimed in claim 2, in which the donor impurity is arsenicand the acceptor impurity is gallium.

4. The method claimed in claim 1, in which the two recited metals arethe same.

References Cited by the Examiner UNITED STATES PATENTS 2,862,840 12/1958 Kordalewski l481.5 3,033,714 5/1962 Ezaki et al 14833.l 3,069,29712/ 1962 Beale 148-185 3,131,096 4/ 1964 Sommers 148-33.:1

DAVID L. RECK, Primary Examiner. HYLAND BIZOT, Examiner.

R. O. DEAN, Assistant Examiner.

1. THE METHOD OF PRODUCING A TUNNEL DIODE COMPRISING THE STEPS OF:ALLOYING A METAL CONTAINING AN IMPURITY OF A GIVEN CONDUCTIVITY TYPE TOA SURFACE REGION OF A SEMICONDUCTOR BODY OF THE SAME TUPE CONDUCTIVITYTO FORM A DEGENERATED SEMICONDUCTOR REGION HAVING A HIGH IMPURITYCONCENTRATION, SAID METAL BEING SELECTED TO BE NON-EUTECTIC WITH SAIDSEMICONDCUTOR BODY; REMOVING A SUBSTANTIAL PORTION OF SAID ALLOY TOEXPOSE THE SAID HIGH IMPURITY CONCENTRATION REGION; AND ALLOYING A METALCONTAINING AN IMPURITY OF THE OPPOSITE CONDUCTIVITY TYPE TO THE SAIDHIGH IMPURITY CONCENTRATION REGION TO FORM A SECOND OPPOSTE TYPE HIGHIMPURITY CONCENTRATION REGION.